A prism sheet having a concave pentagonal structure is disclosed. The prism sheet comprises a base layer, and a prism array disposed on and supported by the base layer. The prism array is composed of a plurality of prisms aligned in parallel and one beside the other. The transversal cross-section of each prism has a shape of concave pentagon, which is symmetrical about a vertical line passing the apex. The interior angle a of the apex is 30°≦α≦120°, the exterior angle β formed by the upper slant side and the lower slant side is β180°, the interior angle γ of the lower vertex formed by the lower slant side and the base is 5°≦γ≦85° and the length w of the base is 30 μm≦w≦100 μm. Preferably, the interior angle α of the apex may be 40°≦α≦100°, the exterior angle β formed by the upper slant side and the lower slant side may be 160°≦β≦179°, and the interior angle γ of the lower vertex formed by the lower slant side and the base may be 30°≦γ≦60°. Preferably, the length w of the base may be 40 μm≦w≦60 μm.
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